Field walking tests are felt to be more reflective of daily living activities than laboratory tests, thereby providing the means to objectively evaluate functional status. An incremental shuttle walking test (ISWT) will first be completed to determine peak walking capacity at week 0: walking speed will initially be set at 0.50m/sec and then increased by 0.17m/sec every minute until the patient reaches a symptom-limited maximum. The endurance shuttle walking test will then be performed at week 0, 12 and 52 to measure change in functional status: subjects will be asked to walk for as long as possible at a constant, predetermined speed corresponding to 85% of peak oxygen uptake, as predicted from the ISWT. The final measure will be the distance covered. Both tests will be completed following recommendations.